The relative widespread and ever increasing use of optical fiber materials as means for carrying optical signals for telecommunications has created a need for devices or tools to cleave the glass of the optical fiber. The cleaved end of the optical fiber should be largely smooth and free from surface imperfections.
When the glass fiber is terminated, light beams travelling into or out of the optical fiber will have a portion of their light reflected from the end face of the fiber. If this reflected light is directed back towards the source of the light beam it will have deleterious effects, including an increase in the optical noise level and possibly disturb the operation of the light source such as a semiconductor laser.
However, if the cleaved end of the fiber is not perpendicular, the reflected light will be directed in a direction away from the incident light beam path and will not affect the light source. Similarly, if light travelling in an optical fiber exits an angled cleaved end of the fiber, for instance in a mechanical splice, then any light reflected from the cleaved end will be directed away from the optical axis of the glass fiber, hence the reflected light will not be guided by, and will not propagate back down, the optical fiber. Consequently, no back-reflection will be observed due to the cleaved end. A cleaved end angled at approximately 6xc2x0-8xc2x0 away from the perpendicular will reduce the back reflection of light in an optical fiber to less than xe2x88x9260 dB.
Applications for angled cleaved ends designed to eliminate back-reflections are found in the pigtailing of optical devices such as semiconductor lasers and in the manufacture of optical coupled fiber Bragg gratings, mechanical splices etc. Suppression of end reflections could also find applications in the design of solid-state laser cavities such as Nd:YAG and in the manufacture of Selfoc lenses. Applicants prior abandoned International Patent Application No PCT/GB96/00919 (published under No WO96/33430) discloses details for the design of a tool for cleaving perpendicular ends onto glass fiber. Other, different, cleaving tools also exist. However, only a few cleaving tools exist which deliberately and controllably cleave angled ends onto optical fiber, including those from York Technology UK and Mars-Actel France. However, these tools require several steps for their operation and hence are difficult to use for an unskilled operator. Both tools tension and twist the fiber before cleaving the fiber with an angled end in the range of 5xc2x0-10xc2x0. The torsion present in the fiber gives angled cleaved ends but with the presence of surface roughness or hackle which becomes more severe with increased fiber end angle. Furthermore, these tools are only capable of angled cleaving a single optical fiber whereas optical fibers are often arranged in the form of a ribbon containing up to 16 fibers.
A further prior art angled cleaving tool is disclosed in U.S. Pat. No. 5,312,468 (Yin et al) in which deflection or bending of the optical fiber or of parallel fibers is effected by displacement of one of a pair of spaced apart fiber clamping means relative to the other in a direction is perpendicular to the axis of the or each fiber. A blade operable between the pair of clamping means effects scoring of the fiber or fibers to initiate angled cleaving at the deflection or bending. An anvil or the like is not employed whilst traction tensioning, or torsion, of the or each fiber is specifically excluded.
In another form of angled cleaving tool disclosed in prior U.S. Pat. No. 5,123,581 (Curtis et al) the fiber is held and tensioned by a pair of spaced apart clamping means and an anvil having an abrupt edge is operable to bear upon the fiber to cause some deflection or bending of it.
An opposing scoring disc or blade slightly offset from the anvil is operable against the fiber to score it and so initiate its angled cleaving. Effective deflection or bending of the fiber takes place between the anvil and blade during scoring so that the clamping means merely perform a fiber clamping and tensioning function.
It is a principal object and purpose of this invention to provide an improved tool capable of compact and simplified construction for cleaving angled ends onto single or multiple optical fibers which can reliably effectuate satisfactory optically flat end faces. These can be in the region of the fiber core or cores with end angles xcex2 in the range of 1xc2x0-20xc2x0 and preferably in the ranges 5xc2x0-10xc2x0 away from the perpendicular to the fiber axis, in order to reduce the back reflection from the cleaved glass surface or surfaces. The cleaved surfaces should be mirror-smooth and largely free from defects in the region of the core of the optical fiber.
It is also desirable to provide an arrangement for cleaving optical fibers at specified and precise distances from the end of the fiber coating or from a constraining device such as a ferrule or connector.
According to this invention a tool for angled cleaving of at least one optical fiber or the like in which a pair of spaced apart clamping means is provided for holding and traction tensioning a length of a said optical fiber or of each such fiber of parallel fibers therebetween, together with anvil means for effecting localised deflection or bending of the length of optical fiber and also blade means for scoring the length of optical fiber in a required sequence of operation of the tool in order to initiate and cause angled cleaving of the length of optical fiber; the tool being characterised by the anvil means having a sharp corner edge for transverse contact with the fiber, which corner edge is closely offset laterally from a corresponding transverse sharp corner edge of a clamp member of one of the clamping means or of a separate part adjacent to said clamp member, said anvil means being operable for controlled close shear force action movement of its corner edge relative to the corner edge of the clamp member or part which latter is or are substantially fixed in the tool apart from slight fiber tensioning movement of the clamp member, whereby localised deflection or bending of the fiber is effected between the respective sharp corner edges in obtaining angled cleaving of the fiber as a result of its scoring by the blade means which is arranged to act against the fiber between said transverse sharp corner edges.